supposed Polarity of Diamagnetic Bodies. 101 



a horseshoe electro-magnet (2381.), making a vibration in less 

 than a second, but with the above condition of the commutator 

 (2675.) gives 4° of deflection due to the induced currents, the 

 magnetic effect being annulled or thrown out. 



2680. Some of the combined effects produced by oblique 

 position of the commutator points were worked out in confir- 

 mation of the former conclusions (2677.). When the commu- 

 tator was so adjusted as to combine any polar power which 

 the bismuth, as a diamagnetic body, might possess, with any 

 conducting power which would permit the formation of cur- 

 rents by induction in its mass (2676.), still the effects were so 

 minute and uncertain as to oblige me to say that, experimen- 

 tally, it is without either polar or inductive action. 



2681. There is another distinction which may usefully be 

 established between the effects of a true sustainable polarity, 

 either magnetic or diamagnetic, and those of the transient 

 induced currents dependent upon time. If we consider the 

 resistance in the circuit, which includes the experimental helix 

 and the galvanometer coil, as nothing, then a magnetic pole 

 of constant strength passed a certain distance into the helix, 

 would produce the same amount of current electricity in it, 

 whether the pole were moved into its place by a quick or a 

 slow motion. Or if the iron core be used (2668.) the same 

 result is produced, provided, in any alternating action, the 

 core is left long enough at the extremities of its journey to 

 acquire, either in its quick or slow alternation, the same state. 

 This I found to be the fact when no commutator nor domi- 

 nant magnet was used; a single insertion of a weak magnetic 

 pole gave the same deflection, whether introduced quickly or 

 slowly; and when the residual dominant magnet, an iron wire 

 core, and the commutator in its position <?, b (2677.) were 

 used, four journeys to and from produced the same effect at 

 the galvanometer when the velocities were as 1 : 5 or even 

 as 1 : 10. 



2682. When a copper, silver, or gold core is employed in 

 place of the iron, the effect is very different. There is no 

 reason to doubt that, as regards the core itself, the same 

 amount of electricity is thrown into the form of induced cir- 

 culating currents within it, by a journey to or from, whether 

 that journey is performed quickly or slowly: the above expe- 

 riment (2681.) in fact confirms such a conclusion. But the 

 effect which is produced upon the experimental helix is not 

 proportionate to the whole amount of these currents, but to 

 the maximum intensities to which they rise. When the core 

 moves slowly, this intensity is small ; when it moves rapidly, 

 it is great, and necessarily so, for the same current of elec- 



